Search

The mid‐lithosphere discontinuity (MLD), identified by a sharp velocity drop at ∼70–100 km depths within the cratonic lithosphere is key to comprehending the chemical composition and thermal structure of the cratonic lithosphere. The MLD is widely accepted to be caused by composition anomalies, such as hydrous minerals, which show low velocities and high electrical conductivities. However, noticeable high‐electrical conductivity anomalies have not been detected in the most cratonic lithosphere. Dolomite has an electrical conductivity similar to olivine and can be originated by carbonatitic melts trapped at ∼80–140 km depths. Here we investigated the elasticity of dolomite under mantle conditions using ab initio calculations and found dolomite exhibits significantly lower velocities than the primary minerals in the lithospheric mantle. Therefore, the dolomite enrichment might provide a good explanation for the observed velocity drop of the MLD in cratonic regions where no high‐conductivity anomaly has been detected, such as the northern Slave craton. Plain Language Summary: Seismological observations have detected a significant mid‐lithosphere discontinuity (MLD) in the cratonic lithosphere, marked by a velocity reduction of ∼2–7% at ∼70–100 km depths. The MLD might reveal the cratonic lithosphere structure and dynamics and its origin is crucial for us to comprehend the formation and evolution histories of cratons. During the formation and evolution of cratons, volatiles‐rich melts can be introduced by the processes of plate subduction or mantle upwelling. Therefore, hydrous minerals and carbonates frozen from volatiles‐rich melts are the pivotal candidates with low velocity. Hydrous minerals usually exhibit high electrical conductivities and their enrichment could cause obvious electrical conductivity anomalies. However, obvious high‐conductivity anomalies have not been detected in many cratonic lithospheres. In contrast, carbonates show electrical conductivity similar to that of olivine, and carbonatitic melts could be trapped at ∼80–140 km depths due to the "decarbonization front" and "redox freezing front," reacting with pyroxene and olivine in the surrounding mantle to produce dolomite as the cratonic lithosphere cools down. Dolomite exhibits significantly lower velocities than the main silicates within the cratonic lithosphere and its enrichment could account for the observed velocity drop at the MLD depths in the cratonic regions where no high‐electrical conductivity anomalies have been found. Key Points: The elasticities of dolomite are determined at P‐T conditions corresponding to the cratonic lithosphere using ab initio calculationsThe velocities of dolomite are significantly lower than those of the main minerals in the lithospheric mantleThe enrichment of dolomite can explain the velocity drop of the mid‐lithosphere discontinuity in cratonic regions without high electrical conductivity anomalies [ABSTRACT FROM AUTHOR]

The Northern Tanzanian Divergence in the East Africa Rift is arguably the best place on Earth to study the controls on rifting of thick lithosphere. Here, where the East Africa Rift intersects the Tanzanian Craton and the Mozambique Belt, the relationships between volcanism, faulting, pre‐existing structures and lithospheric thickness and composition can be observed. In this work, we carry out the first lithospheric‐scale 3D magnetotelluric modeling of the Northern Tanzanian Divergence and combine the results with experimental electrical conductivity and petrology models to calculate mantle composition, which is also inferred in the craton from reanalysis of garnet xenocryst data. Our results show that metasomatic materials exist in the cratonic lithospheric mantle and the relatively undeveloped southern part of the rift zone. However, the lithospheric mantle of the Mozambique Belt and the more developed northern section of the rift is more resistive and does not contain metasomatic phases. Combined with geochemical data from erupted lavas, these results suggest that, in zones that have experienced voluminous Cenozoic magmatism, melting events have destroyed the metasomes and dehydrated the mantle. Since the presence of magma is a primary control of lithospheric strength, rifting may become limited as the lithospheric mantle becomes dehydrated and harder to melt. Plain Language Summary: The motion of tectonic plates relies on a specific set of physical conditions. Continental breakup or rifting occurs when certain parts of the lithosphere are weak, and when stress applied to these regions is sufficient. Weaknesses in the lithosphere rely on its composition and pre‐existing structures. We can image and analyze these features using the magnetotelluric method, a geophysical technique that maps electrical conductivity variations within the Earth. Our results show that compositionally weakening agents (metasomes) play an essential role in the development of the rift by making the mantle easier to melt. We also image some portions of the rift that do not contain such agents, suggesting that melts may have dried out these parts of the lithosphere, leaving a dry and resistive residue. This situation may indicate that melting in the region might be limited in the long run due to the absence of these materials. Key Points: 3D magnetotelluric models of North Tanzanian Divergence are converted to water in mantle models to map metasomatism in the regionMelting events in the Mozambique Belt caused metasomes to be destroyed and the lithospheric mantle to be dehydratedThe rifting in the region might be limited if there is no supply of metasomatic material toward the rift zone [ABSTRACT FROM AUTHOR]

The structurally controlled copper–gold (Cu–Au) mineralization in the Suwara area in the southern part of the Bundelkhand craton, Central India, is hosted within quartz reefs traversing older granitoids. Mineralization is distinctly associated with hydrothermal alteration (potassic, chloritic and iron alteration in the ore zone and Kmetasomatism in the wall rocks). Field observations and laboratory evidence confirm the Fe–Cu–Au association in the study area. Sulphide mineralization is represented by pyrite, chalcopyrite, covellite, chalcocite and bornite occurring as disseminations, stringers and specks within the altered quartz veins, with gold occurring as fine isolated disseminations within quartz and iron oxides. Chemical analysis of surface and subsurface samples showed promising values for Cu (up to 1.0%) and Au (up to 450 ppb) content. Fluid inclusion studies indicated the occurrence of saline mineral fluids (Na– K–Cl-bearing) with the presence of H2O–CO2–CH4 in the mineral system. Overall characteristics of the mineralization and alteration patterns of the prospect indicate that it probably belongs to an iron oxide–copper–goldtype set-up for mineralization. The present study on Cu–Au mineralization from the southern Bundelkhand craton will have significant implications for further exploration and research in the area. [ABSTRACT FROM AUTHOR]

Highly altered granitoids in the western part of Bundelkhand craton around Kanchanpur and Thuni villages in Shivpuri district, Madhya Pradesh, India, are significantly associated with copper-molybdenum-tungsten mineralization which is manifested as stringers, blebs, clots and fine specks of chalcopyrite, pyrite, molybdenite and scheelite and as vein-fillings associated with hydrothermal alteration within the ore zone and adjacent host rocks. The cumulative strike length of the zone of mineralization (NW-SE) and associated alteration is around 3.5 km. Various mineral assemblages, viz. Kfeldspar-biotite-chlorite, K-feldspar-sericite-chlorite and quartz-epidote-chlorite-sericite indicate intense hydrothermal alteration in the area. Analytical results have shown anomalous values for Cu (up to 1530 ppm), Mo (up to 4080 ppm) and W (up to 1449 ppm). Field observations and chemical analysis have been further supplemented by ore microscopic, petrographic, geochemical and EPMA studies to identify sulphide phases (of Fe, Cu and Mo) and scheelite. All the field and laboratory studies collectively indicate a probable hydrothermal origin of mineralization in the study area. The present study on Cu, Mo and W mineralization of economic grade in the western Bundelkhand craton has important implications for further metallogenic studies and mineral exploration in the area. [ABSTRACT FROM AUTHOR]

Abstract Mid‐lithosphere discontinuities are seismic interfaces likely located within the lithospheric mantle of stable cratons, which typically represent velocities decreasing with depth. The origins of these interfaces are poorly understood due to the difficulties in both characterizing them seismically and reconciling the observations with thermal‐chemical models of cratons. Metasomatism of the cratonic lithosphere has been reported by numerous geochemical and petrological studies worldwide, yet its seismic signature remains elusive. Here, we identify two distinct mid‐lithosphere discontinuities at ∼87 and ∼117 km depth beneath the eastern Wyoming craton and the southwestern Superior craton by analyzing seismic data recorded by two longstanding stations. Our waveform modeling shows that the shallow and deep interfaces represent isotropic velocity drops of 2%–8% and 4%–9%, respectively, depending on the contributions from changes in radial anisotropy and density. By building a thermal‐chemical model including the regional xenolith thermobarometry constraints and the experimental phase‐equilibrium data of mantle metasomatism, we show that the shallow interface probably represents the metasomatic front, below which hydrous minerals such as amphibole and phlogopite are present, whereas the deep interface may be caused by the onset of carbonated partial melting. The hydrous minerals and melts are products of mantle metasomatism, with CO2‐H2O‐rich siliceous melt as a probable metasomatic reagent. Our results suggest that mantle metasomatism is probably an important cause of mid‐lithosphere discontinuities worldwide, especially near craton boundaries, where the mantle lithosphere may be intensely metasomatized by fluids and melts released by subducting slabs.

Potassium sulfide KFeS2 (hanswilkeite) has been identified in polymineralic inclusions in a diamond from the Udachnaya kimberlite pipe (Siberian craton, Yakutia). This is the second occurrence of hanswilkeite in nature and the first one in mantle-derived samples. Sulfide KFeS2 is monoclinic, the space group—C 2/c. Its crystal structure consists of chains with K in the interstices. The tetrahedra are centered by iron ions and linked by edges, thus forming chains of [FeS2] frameworks. The strongest lines of the electron diffraction powder pattern are 7.05 Å—(200); 5.34 Å (0 2 ¯ 0); and 3.05 Å (2 2 ¯ 0), and the angles between directions are <2 2 ¯ 0/0 2 ¯ 0>—60° and <2 2 ¯ 0/200>—30°. KFeS2 has been found as a discrete phase within polymineralic inclusions consisting of apatite, ilmenite, chondrodite, phlogopite, dolomite, and a fluid phase. The data obtained from the composition of the hanswilkeite (KFeS2) inclusion and other rare minerals (chondrodite, Mg-apatite, Cr-ilmenite) in primary inclusions in a diamond from the Udachnaya kimberlite testify to the important role of metasomatic processes in diamond formation. [ABSTRACT FROM AUTHOR]

Abstract The Paramirim Aulacogen was filled by the Espinhaço and São Francisco supergroups in the period from 1.75 to 0.69 Ga, and suffered partial inversion during the Ediacaran. In the northern sector of the intracontinental domain of the Araçuaí-WestCongo Orogen, six compressive deformational phases were interpreted and associated with the frontal inversion of the Paramirim Aulacogen. Three structural domains were identified: Jacaraci Fold-Thrust Belt, Caetité Nappe, and Transpressive Domain. The nucleation of deformational structures is related to a maximum stress field with general WSW-ENE orientation. The first deformational phase (D1), found in the Jacaraci Fold-Thrust Belt and the Transpressional Domain, is related to the evolution of the Rio Pardo Salient. A dextral transpressional system nucleated the Caetité Nappe. This system also juxtaposed amphibolite facies rocks over lower temperature facies, as well as Statherian over Tonian rocks. Furthermore, this system was responsible for deformation in the transpressional domains and late deformation in the Jacaraci Fold-Thrust Belt. The region presents a variety of structures and is, therefore, an excellent natural laboratory for studying positive inversion in aulacogens.

New measurements shear-wave splitting (SWS) were determined using a teleseismic dataset from 21 broadband seismic stations belonging to the GSN-BX network in Botswana archived at IRIS-DMC. The stations are distributed across major geologic terrains such as the Kaapvaal craton, Limpopo Mobile Belt and Zimbabwe Craton. Earthquakes with magnitude larger than 5.2 mb with epicentral distances in the range of 90° and 180° were analyzed for SKS (S-wave traversing the core as P-wave) and SKKS (S-wave traversing the core as P-wave with one reflection from inner side of the Core Mantle Boundary) phases, while PKS (P-wave bottoming in the core and converting to S-wave at the Core Mantle Boundary) phases were analyzed in the range of 130°–165°. SWS parameters were calculated at each station by minimizing the energy on the transverse component of the PKS, SKKS, and SKS phases (hereafter collectively called XKS). The measurement included the polarization direction ϕ, which gives a reliable indication of the alignment of olivine in the upper mantle, and, the delay time dt between the arrival times of the fast and slow travelling split shear waves. The value of dt is related to the intrinsic anisotropy and thickness of the anisotropic layer. The SWS parameters provide insights into the present and past deformation processes of upper mantle.

Recent studies have shown that biosignatures of ancient microbial life exist in mineral coatings in deep bedrock fractures of Precambrian cratons, but such surveys have been few and far between. Here, we report results from southwestern Sweden in an area of 1.6–1.5 Ga Paleoproterozoic rocks heavily reworked by the 1.14–0.96 Ga Sveconorwegian orogeny, a terrane previously scarcely explored for ancient microbial biosignatures. Calcite‐pyrite‐adularia‐illite‐coated fractures were analyzed for stable isotopes via Secondary Ion Mass Spectrometry (δ13C, δ18O, δ34S) and in situ Rb/Sr geochronology via Laser‐ablation inductively coupled plasma mass spectrometry. The Rb/Sr ages for calcite‐adularia and calcite‐illite show that several fluid flow events can be discerned (797 ± 18–769 ± 7, 391 ± 5–387 ± 6, 356 ± 5–347 ± 4, and 301 ± 7 Ma). The δ13C, δ18O and 87Sr/86Sr values of different calcite growth zones further confirmed episodic fluid flow. Pyrite δ34S values down to −49.9‰V‐CDT, together with systematically increased δ34S from crystal core to rim, suggest formation following microbial sulfate reduction under semi‐closed conditions. Assemblages involving MSR‐related pyrite generally have Devonian to Permian Rb/Sr ages, indicating an association to extension‐related fracturing and fluid mixing during foreland‐basin formation linked to Caledonian orogeny in the northwest. An assemblage with an age of 301 ± 7 Ma is potentially related to Oslo Rift extension, whereas the Neo‐Proterozoic ages relate to post‐Sveconorwegian extensional tectonics. Remnants of short‐chained fatty acids in the youngest calcite coatings further indicate a biogenic origin, while the absence of organic molecules in older calcite is in line with thermal degradation, potentially related to heating during Caledonian foreland basin burial. Plain Language Summary: This study investigates mineral coatings in Proterozoic basement fractures of Southwestern Sweden, within the Precambrian Fennoscandian shield, to gain insights into ancient microbial life and paleo‐fluid flow. Isotopic signatures of these mineral coatings suggest that microbial sulfate reducers have been present in the system as also indicated by preserved organic molecules. Microanalytical geochronology determinations reveal that the fracture system has been activated several times in the Neoproterozoic, Devonian‐Early Carboniferous, and Late Carboniferous/Early Permian. These activations are associated with extension events following the Sveconorwegian and Caledonian orogenies as well as formation of the Oslo Rift. The signs of microbial activity are related to the youngest of these events, post‐dating burial in the Caledonian foreland basin, when bedrock temperatures became habitable. Key Points: Rb/Sr geochronology of calcite veins detects several generations of fracture activation and fluid flow in Paleoproterozoic basement rocksSubstantial δ34S variation and preserved fatty acids suggest that microbial sulfate reduction has been active in the fracture systemMicrobial activity relates to Paleozoic fracture activation in relation to Caledonian orogeny/foreland basin and later extensional events [ABSTRACT FROM AUTHOR]

The Paramirim Aulacogen was filled by the Espinhaço and São Francisco supergroups in the period from 1.75 to 0.69 Ga, and suffered partial inversion during the Ediacaran. In the northern sector of the intracontinental domain of the Araçuaí-WestCongo Orogen, six compressive deformational phases were interpreted and associated with the frontal inversion of the Paramirim Aulacogen. Three structural domains were identified: Jacaraci Fold-Thrust Belt, Caetité Nappe, and Transpressive Domain. The nucleation of deformational structures is related to a maximum stress field with general WSW-ENE orientation. The first deformational phase (D1), found in the Jacaraci Fold-Thrust Belt and the Transpressional Domain, is related to the evolution of the Rio Pardo Salient. A dextral transpressional system nucleated the Caetité Nappe. This system also juxtaposed amphibolite facies rocks over lower temperature facies, as well as Statherian over Tonian rocks. Furthermore, this system was responsible for deformation in the transpressional domains and late deformation in the Jacaraci Fold-Thrust Belt. The region presents a variety of structures and is, therefore, an excellent natural laboratory for studying positive inversion in aulacogens. [ABSTRACT FROM AUTHOR]

[Display omitted] • Whole-lithosphere mapping reveals extensive Proterozoic reworking of the lithosphere. • The lithospheric mantle was refertilised by magmatic events at ∼2.06 Ga and ∼1.08 Ga. • Refertilisation precedes basin formation during recratonisation over 200–400 Ma. • Geodynamic linkages are proposed with the assembly phase of supercontinent cycles. • Supercontinent-phase is an important condition for evolution of cratonic lithosphere. Knowledge of the evolution of ancient cratonic lithospheres underpins our understanding of Precambrian Earth. The Yilgarn Craton has exceptionally well-preserved Archean geology, with juvenile crust formation and major orogenesis concluding in the Neoarchean, and a stabilised upper-crustal architecture developing before 2.42 Ga. However, in an apparent dichotomy, geophysical models resolve lithospheric mantle composition outside the range of xenolith data from Archean regions, indicating the lithospheric mantle has since been extensively refertilised. Post-Archean igneous and sedimentary rocks record a prolonged lithospheric evolution that is not well resolved in datasets recording bulk crustal isotopic evolution. Reconciling these, we combine interpretation of geological and geophysical data to resolve two phases of lithosphere destabilisation driven by major magmatic events at ∼2.06 Ga and at ∼1.08 Ga. During destabilisation, sub-lithospheric and sub-crustal mantle fluxes caused extensive mantle refertilisation. For 200–400 Ma post-refertilisation, distributed sedimentary basins formed during recratonisation of the now denser lithosphere. The timing of these events suggests a relationship with the early stages of supercontinent assembly: Dominant downwelling beneath the assembling supercontinent sustains a sufficiently non-tensile tectonic setting to inhibit lithospheric thinning and breakup and enhances lateral flow of any upwelling mantle. This setting allows widespread intraplate refertilisation to occur while later the assembled supercontinent provides a stable setting allowing thermal re-equilibration and recratonisation to occur. In contrast, lithospheric refertilisation during supercontinent breakup will be more susceptible to density instabilities and recycling in later collisions. Consequently, we suggest that refertilisation of extant cratonic lithosphere may dominantly have occurred during the assembly of supercontinents. [ABSTRACT FROM AUTHOR]

Cratons formed due to the specific melting regime of the primitive mantle with elevated mantle temperature during Archean. However, each craton has undergone a distinct evolution history, and some have lost their stability. To investigate to what degree cratons in comparison with one another have been modified from their analogous initial form, we employed Sn-Pn differential (PSn) traveltimes to derive Vp/Vs ratio, which is thought to be related to Mg# of the uppermantle. We assessed Pn, Sn, and PSn data using three datasets based on epicentral distance: (1) 2°–12°, (2) 2°–7°, and (3) 7°–12°. The results suggest that most cratons show comparable seismic properties with high velocities and low Vp/Vs ratio, implying a highly depleted uppermost mantle that resembles the original residue from the partial melt extraction of the primitive mantle during the Archean. Conversely, the Eastern North China Craton (ENCC) displays the lowest P- and S-wave velocities, and noticeable high Vp/Vs ratios in all datasets, implying a systematic difference with other cratons. This observation suggests a scenario of total removal of the depleted Archean mantle lithosphere beneath the ENCC. In contrast, the Ordos Block located at the western part of the North China Craton (WNCC) shows velocities and Vp/Vs ratio comparable with those of the typical cratons, suggesting that it has still maintained its Archean mantle lithosphere. The Wyoming Craton has a high Vp/Vs ratio similar to that of the ENCC and a high P-wave velocity comparable to that of the typical cratons. These features suggest that the Archean mantle lithosphere has been significantly modified rather than totally removed and replaced by a younger fertile mantle. The Indian Craton presents a low Vp/Vs ratio and comparatively high velocities at shallow parts of the mantle lithosphere but a high Vp/Vs ratio at deeper parts similar to that of the ENCC, suggesting a partial modification of the Indian Craton at deeper parts. [ABSTRACT FROM AUTHOR]

The Middle – Dnieper megablock, which is a fragment of archean craton, differs from other cratons on Earth by a large variety of Archean granitoids (Tok, Mokro-Moscowka, and Demurino complexes) which were formed later than the Mesoarchean TTG of sura complex. In this regard, the Middle – Dnieper megablock is an important area for studying the genesis and geodynamic conditions of Late Archaean granitoid formation. The poorly studied Late Archean granitoids in the Middle – Dnieper block include the Hannivka granites in the East Hannivka monocline of the Kryvyi Rig – Kremenchuk structure, the age and stratigraphic position of which have been the subject of a long debate. The aim of the work is to determine geochemical peculiarities. genesis and U-Pb age of Hannivka granites and to compare them with other archean granitoid complexes of the Middle-Dnieper fragment of the Mesoarchean craton. The LA-ICP-MS method determined the U-Pb age of zircon from Hannivka granite 2827 ± 16 Ma. They are close in time to the granitoids of the Tok and Mokro-Moscowka complexes and were formed much later than the granitoids of the Demurino complex. The Hannivka granites could have been formed in a crustal magmatic source as a result of melting of an older crust. They differ from other Archaean granitoids of the Middle-Dnieper megablock by the increased content of U (56.4 ppm) and the presence of Mo (4.3 ppm). Unsolved problems that require further study include determination of the connection of Hannivka granites with granitoid intrusions of the Mokra-Moscowka and Tok complexes outside the Eastern Hannivka structure and the origin of ore mineralization for uranium and molybdenum.

Despite being exposed to convective stresses for much of the Earth's history, cratonic roots appear capable of resisting mantle shearing. This tectonic stability can be attributed to the neutral density and higher strength of cratons. However, the excess thickness of cratons and their higher viscosity amplify coupling to underlying mantle flow, which could be destabilizing. To investigate the stresses that a convecting mantle exerts on cratons that are both strong and thick, we developed instantaneous global spherical numerical models that incorporate present‐day geoemetry of cratons within active mantle flow. Our results show that mantle flow is diverted downward beneath thick and viscous cratonic roots, giving rise to a ring of elevated and inwardly‐convergent tractions along a craton's periphery. These tractions induce regional compressive stress regimes within cratonic interiors. Such compression could serve to stabilize older continental lithosphere against mantle shearing, thus adding an additional factor that promotes cratonic longevity. Plain Language Summary: Cratons are the oldest continental relicts on Earth. Due to plate tectonics and mantle convection, many non‐cratonic rocks get recycled. However, cratons have escaped tectonic recycling, and some have remained stable for more than ∼3 billion years. Previous studies have shown that cratons' high strength and neutral buoyancy provide them with tectonic stability. Here we show that the deep roots of cratons also help to stabilize them. This is because mantle flow is deflected downward beneath thick cratonic roots, and this deflection generates a ring of inwardly‐directed forces around the edges of the craton. These inward forces compress the craton interior. Such self‐induced compressive stresses may further help to stabilize Earth's oldest lithosphere. Key Points: Mantle flow leads to inwardly convergent tractions around the edges of cratons, and compressive stress withinConvergent tractions result from the downward diversion of mantle flowThis convective self‐compression could help stabilize older lithosphere against convective erosion [ABSTRACT FROM AUTHOR]

The Tibetan Plateau, induced by the India-Eurasian collision, has the highest average altitude in the world. During its uplift vertically, the Tibetan Plateau has been considered to expand laterally. However, there are several strong and almost non-deformable cratons on its periphery, such as the Tarim, North China craton, and South China block. The present landform features show that these cratons limit the expansion of the Tibetan Plateau. However, there is still much controversy over whether the deformation can be transmitted to periphery orogens or reactivate ancient orogens in the cratons. This study used numerical models to investigate the effect of rheological heterogeneities on the lithospheric deformation of the Tibetan Plateau and its neighbouring regions. The results show that the lateral heterogeneities of the lithosphere have an important influence on the deformation or strain partitioning. Generally, during the lateral expansion of the Tibetan Plateau, its peripheral cratons can transmit the deformation or high strain to neighbouring weak orogens. This case can be used to understand the Tian Shan orogen, which was reactivated by the India-Eurasian collision. However, when the orogens inside the cratons have high lithospheric strength, high strain is difficult to distribute on them and the expanding Tibetan Plateau is constrained by its peripheral cratons. These results can be used to explain the ancient orogens that are not strongly deformed, such as the Jiangnan orogen in the South China block. Because these orogens formed at the same time as the cratons and have relatively high lithospheric strength. In addition, the large lithospheric thickness difference and low crustal rheological contrast favor high strain rates localized on the lithosphere of the ancient orogen in the craton, such as the Trans-North China orogen in the North China craton.

Abstract Despite being exposed to convective stresses for much of the Earth's history, cratonic roots appear capable of resisting mantle shearing. This tectonic stability can be attributed to the neutral density and higher strength of cratons. However, the excess thickness of cratons and their higher viscosity amplify coupling to underlying mantle flow, which could be destabilizing. To investigate the stresses that a convecting mantle exerts on cratons that are both strong and thick, we developed instantaneous global spherical numerical models that incorporate present‐day geoemetry of cratons within active mantle flow. Our results show that mantle flow is diverted downward beneath thick and viscous cratonic roots, giving rise to a ring of elevated and inwardly‐convergent tractions along a craton's periphery. These tractions induce regional compressive stress regimes within cratonic interiors. Such compression could serve to stabilize older continental lithosphere against mantle shearing, thus adding an additional factor that promotes cratonic longevity.

The Middle-Dnieper megablock, which is a fragment of the craton, differs from other cratons found on Earth. This is because of the large variety of granitoids (Tokiv, Mokro-Moskowka, and Demuryne complexes) in the former that were formed after the Mesoarchean TTG. Thus, the Middle-Dnieper megablock is important for studying the genesis and geodynamic formation conditions of Late Archaean granitoids. The granitoids in the Middle-Dnieper megablock are not well understood. They include the Hannivka granites of the East Hannivka monocline of the Kryvyi RihKremenchuk structure, whose age and stratigraphic position has been a matter of a long-standing debate. The purpose of the work is to study the geochemistry, genesis and U-Pb age of the Hannivka granites. Based on our results, the Hannivka granites possibly formed in the crust resulting from the melting of older rocks. They differ from other Late Archean granitoids of the Middle-Dnieper megablock by their high U (56.4 ppm) content and the presence of Mo (4.3 ppm). The Hannivka granites underwent tectonic reworking during a collisional event about 2.0 billion years ago, which is probably associated with the kalishpatization of these rocks. The U-Pb age of the cores of zircons sampled from the Hannivka granites, determined by LA-ICP-MS method, are about 2827±16 million years in age. Younger rims probably formed during kalishpatization. The Hannivka granites are the same age as the granitoids of the Mokro-Moskowka and Tokiv complexes. Late Archean granitoids were formed between 2.99-2.7 Ga in the Middle-Dnieper granite-greenstone block and in the geologically similar granite-greenstone block KMA are 2.6 Ga in age. In the Pilbara craton, which is a Paleoarchean granite-greenstone complex, the age of biotite and feldspar granites is similar to the age of the rocks on the Middle-Dnieper megablock (2.94-2.93 Ga). The difference in magmatism ages may be due to the drift of the different cratons above mantle plumes of different ages. [ABSTRACT FROM AUTHOR]

Coupled U‐Pb and trace‐element analyses of accessory phases in crustal xenoliths from the Late Devonian Udachnaya kimberlite (Siberian craton, Russia) are used to constrain Moho temperature and crustal heat production at the time of kimberlite eruption. Rutile and apatite in lower‐crustal garnet granulites record U‐Pb dates that extend from 1.8 Ga to 360 Ma (timing of kimberlite eruption). This contrasts with upper‐crustal tonalites and amphibolites that contain solely Paleoproterozoic apatite. Depth profiling of rutile from the lower‐crustal xenoliths show that U‐Pb dates increase gradually from rim to core over μm‐scale distances, with slower‐diffusing elements (e.g., Al) increasing in concentration across similar length‐scales. The U‐Pb and trace element gradients in rutile are incompatible with partial Pb loss during slow cooling, but are consistent with neocrystallization and re‐heating of the lower crust for <1 Myr prior to eruption. Because Paleoproterozoic rutile and apatite dates are preserved, we infer that long‐term ambient lower‐crustal temperatures before this thermal perturbation were cooler than the Pb closure temperature of rutile and probably apatite (<400°C). The lower‐crustal temperature bounds from these data are consistent with pressure‐temperature arrays of Udachnaya peridotite xenoliths that suggest relatively cool geothermal gradients, signifying that the mantle xenoliths accurately capture the thermal state of the lithosphere prior to eruption. Combined, the xenolith data imply low crustal heat production for the Siberian craton (∼0.3 μW/m3). Nevertheless, such values produce surface heat flow values of 20–40 mW/m2, higher than measured around Udachnaya (average 19 mW/m2), suggesting that the surface heat flow measurements are inaccurate. Plain Language Summary: The decay of radioactive elements, like uranium (U), thorium (Th), and potassium (K), produces heat and the dissipation of this heat from Earth's interior drives flow at depth and the movement of tectonic plates at the surface over geologic time. The crust—the planet's rocky outer layer—is hypothesized to contain a significant portion of Earth's heat‐producing elements, yet this budget is uncertain. The total amount of heat leaving the surface can be measured, but how much of this flux reflects heat production within the crust versus heat derived from the underlying mantle is also uncertain. Kimberlite pipes carry fragments of Earth's interior to the surface ("xenoliths") in Siberia. Some of the xenoliths are from near the base of the crust, and temperature‐sensitive chronometers in these rocks record ancient dates (>1 billion years old). Such ancient dates are significant because they can only be preserved if temperatures in the deep crust were cool (<400°C). Models of heat transfer through the Siberian crust using our results and mantle xenolith pressure‐temperature data indicate relatively low heat production in the crust. Key Points: The U‐Pb system in deep crustal xenoliths is sensitive to transient heating of the lower crust and not just slow coolingThe central Siberian craton lower crust resided below the Pb closure temperature of rutile and apatite prior to kimberlite eruption 360 MaExtremely low crustal heat production for the craton (∼0.3 μW/m3) is consistent with peridotite xenolith P‐T data [ABSTRACT FROM AUTHOR]

Exploration and development practices prove that intracratonic strike–slip faults control the development of carbonate reservoirs and the enrichment of oil and gas in the Tarim Basin. Intracratonic strike–slip faults are characterized by short displacement, small throw and great burial depth, so there are still many controversies on their structural evolution and formation mechanisms. In order to settle these controversies, this paper firstly analyzes the geometric and kinematic characteristics of the intracratonic strike–slip faults in the central Tarim Basin. Then, based on extensive high-accuracy 3D seismic data and 2D seismic data, the formation and evolution process of the intracratonic strike–slip faults in the Tarim Basin are discussed deeply, and their genetic mechanisms are explored. Moreover, the following research results are obtained. First, the strike–slip faults in the study area have the characteristics of vertical stratification, plane zonation and segmentation along the strike. Second, the movement directions of the deep transpressional strike–slip faults are simple. The NE and NNE strike–slip faults are sinistral, and the NNW strike–slip faults are dextral. However, the shallow transtensional faults are more different in the movement direction. The strike–slip faults have displacements of 400–1500 m, and they are classified as intracratonic strike–slip faults with small slip distance. Third, the strike–slip faults were formed in the middle Caledonian, and some faults were reactivated in the late Caledonian–early Hercynian, late Hercynian, and Yanshanian–early Himalayan. The distribution of faults is different in different periods. Fourth, the formation of the strike–slip faults in the middle Caledonian is controlled by the basement heterogeneity and the compression action from the closure and subduction of the Proto-Tethys Ocean. The transtensional faults are R-shear branch faults or tensile break faults generated by the later activation of middle Caledonian strike-slip faults, and their formation is controlled by the subduction and closure of oceanic basins around the basins in different periods. In conclusion, the structural characteristics, formation & evolution and genetic mechanisms of intracratonic strike–slip faults are in close relation to oil and gas, where great benefit of oil and gas exploration and development is achieved. Besides the Tarim Basin, the Sichuan Basin and the Ordos Basin have similar geological and structural settings, so the studies on typical basins will surely enrich and complete the theories on the intracratonic strike–slip faults in domestic micro land blocks and multi-cycle basins and point out the direction for the discovery of more oil and gas resource.

Strike-slip faults, proven to be closely linked to hydrocarbon migration and accumulation, are widespread in the Tarim Basin Craton. Deformation patterns in the eastern part of the Central Uplift Belt of the Tarim Basin are analyzed in detail to understand the deformation model and genetic mechanism of strike-slip faults, how their patterns impact reservoir formation and influence oil and gas potential. Regional tectonic events are taken into consideration to identify the primary factors that controlled the development of strike-slip faults in the region. The Tazhong Uplift in the eastern part of Central Uplift Belt is believed to be a complex anticlinal uplift formed by compression-and-torsion acting on the Cambrian – Middle Ordovician platform during the middle–late Caledonian period. Multi-stage development of this north-trending fault–fold belt and the NE-trending strike-slip faults make it structurally complex. The NE-trending Paleozoic strike-slip faults were formed jointly by the differential thrusting of the Tazhong Uplift along Fault No. I and the NE-trending shear sliding of the basal fault blocks during the middle–late Caledonian – early Hercynian. Based on the distribution of effective source rocks, the tectonic setting during the period critical to hydrocarbon accumulation, and the distribution of conductive faults, the northern slope of the Tazhong Uplift— especially its west-central part where the NE-trending faults are developed is not only located close to the northern hydrocarbon source rock area but also possesses conditions suitable for the development of carbonate reservoirs. In addition, the NE-trending faults provide passage for initial development of the reservoir and the subsequent migration of oil and gas from the Aman area to the uplifted zone, making the Tazhong Uplift an extremely favorable area for oil and gas accumulation with substantial potential for exploration.

The structure and dynamics of the upper mantle control tectonics, seismicity, magmatism, and the development of mineral deposits. Seismic tomography maps spatial variations in seismic velocity and offers essential information on the variations of temperature in the mantle, the thickness and mechanical strength of the lithosphere, and the convection patterns below it. Thanks to the growth in the station coverage, tomographic models of Asia reveal increasingly detailed structures, in particular in its best-sampled parts. Here, we present a new waveform tomography model, ASIA2024 , constrained by massive global and regional datasets. The data coverage used to construct ASIA2024 is maximised across the hemisphere centred at Asia. In China, in particular, dense national network data enhances the sampling. Our waveform tomography extracts structural information from surface waves and from S and multiple S body waves. The effects of errors are suppressed by statistical and targeted outlier analyses and the removal of the least mutually consistent data. Extensive comparisons of contemporary tomographic models reveal both consensus features and differences between models and demonstrate relative advantages of different approaches and data types. ASIA2024 advances the resolution of the imaging compared to the state of the art at the scale of the continent. A prominent high-velocity anomaly at lithospheric depths shows the Indian cratonic lithosphere underthrusting and subducting beneath Tibet. In the transition zone below the plateau, a fragmented high-velocity anomaly indicates lithospheric remnants, probably from different phases of subduction. The lithosphere beneath most diamondiferous kimberlites—originally emplaced on thick cratonic lithosphere—is observed to be still thick at present. Relatively low velocities at kimberlite locations are indicative of craton-lithosphere thinning and are detected beneath northwestern Siberian Craton (Siberian Traps) and most of the Indian Shield (Deccan Traps and surroundings), with the exception of the intact cratonic lithosphere beneath northeastern Dharwar Craton. This suggests that the mantle plumes responsible for the traps have eroded the deep cratonic lithosphere. Thin lithosphere and recent basaltic volcanism are observed in eastern Sino-Korean and Yangtze Cratons, with subduction, stretching, and rifting likely to have weakened and modified their cratonic roots. Cenozoic basalts are found exclusively where the lithosphere is observed to be thin. Beneath the Hainan volcanic region, a low-velocity anomaly is observed throughout the upper mantle, consistent with the previously proposed Hainan Plume feeding the magmatism. The shape of the anomaly indicates a complex morphology of the upwelling. Low-velocity anomalies in the mantle transition zone beneath the Hangai Dome and southern Siberian Craton are consistent with hot upwelling(s) and horizontal asthenospheric flow feeding the dispersed basaltic volcanism. Sediment-hosted metal deposits tend to be located near contrasts in the thickness of the lithosphere, including craton boundaries and other substantial heterogeneities. Intraplate seismicity is controlled by plate-boundary stresses and lateral variations of the lithospheric thickness and strength. Areas with relatively thin lithosphere across Asia tend to localise deformation and seismicity. The Gujarat seismic zone in India is collocated with an area of warm, thin lithosphere. This suggests a relationship between the occurrence of devastating earthquakes there and deformation in the mechanically weak part of the plate. [Display omitted] • Seismic tomography maps the structure of Asia's upper mantle in increasing detail. • Our new waveform tomography model, ASIA2024 , advances the resolution of the imaging. • Mantle lithosphere exerts primary controls on tectonics, seismicity and magmatism. • Lithospheric thickness and plate boundary stresses control intraplate seismicity. • Evolution of continental lithosphere is evidenced by mantle structure and volcanism. [ABSTRACT FROM AUTHOR]

[Display omitted] • No modern style, Benioff-type subduction operated in the Archean. • Shuffle tectonics substitute for subduction with fluxed mantle melting, but mostly in off-craton regions. • Regions of early rifting paved the way for crustal preservation through melt extraction, accompanied by dehydration stiffening, giving rise to later cratons. • In regions of today's cratons, TTG magmatism was predominant, whilst early subduction-like magmatism only occurred outside of these zones. Subduction is a key geodynamic feature on modern Earth that drives crustal chemical diversity, bridging the atmo-, hydro-, and lithosphere, but remains an enigmatic, unique planetary feature. Indisputable is the critical role of subduction in shaping Earth's geomorphology and crustal dichotomy (ocean vs continental crust) and its impacts on long-term climate, making it arguably the most important process on present-day Earth across all geosciences. It is thus important to understand to what degree, or if at all, subduction was operational during the billions of years that led to our geological status quo. Here, we assess the feasibility of Archean subduction with a focus on early Earth geodynamics. We argue that convection-driven rifting, but not spreading, formed the first keels under the primordial crust, providing the necessary stability for crustal survival. These sections of crustal rejuvenation would counterintuitively forge the first stable proto-cratonic terranes, which later evolved into cratons. Hydrated upper crustal rocks were vital in generating early fluxed mantle melting and related volcanism, but also for partial melting in hydrated lower crustal sections within proto-cratons, giving rise to tonalite-trondhjemite granodiorites (TTGs). Both processes operated off- and on-craton, respectively, and required melting of hydrated crust and crustal convergence but are unrelated. Away from proto-cratonic regions of minor episodic divergence and rifting, relative motions were accommodated by convergence and shuffle tectonics, leading to Archean-style subduction in localised regions that were prone to destruction. This primitive form of subduction and crustal maturation has operated from the earliest Archean time in a plate-and-lid regime. Crucially, this 'Archean subduction' represents short-lived crustal shuffle-tectonics outside areas of today's cratons with fluxed melting in upper mantle regions but does not resemble present-day Benioff-style subduction. The development of subduction akin to present-day processes towards the end of the Archean could plausibly have driven atmospheric oxygenation over a few hundred million years between ca. 2.8–2.3 Ga, with H-loss to space accompanied by atmospheric oxidation through subduction-related global volcanic SO 2 emissions. [ABSTRACT FROM AUTHOR]

The article describes the history of studying the diamond content of tectonic structures of the territory of Belarus. Based on the results of magnetometric, mineralogical, tectonic studies carried out by industrial geologists and scientists over the past 50 years, new scientifically substantiated criteria for the search for explosion pipes have been developed using Clifford’s rule, according to which kimberlite explosion pipes are developed within the Archean cratons, where the thickness of the lithosphere is 175–270 km, and are absent in the zones of Early Proterozoic stabilisation and tectonomagmatic activation. Explosion tubes on the African-Arabian, East Siberian, Sino-Korean and East European platforms demonstrate their confinement to the Archean cratons and may be associated with zones of paleosubduction of the Proterozoic oceanic crust beneath the Archean cratons. Based on this, the authors scientifically substantiated the hypothesis that during the closure of the Early Proterozoic paleoocean separating the Fenno-Scandinavian craton from the Volga-Ural and Sarmatian cratons, subduction of the younger crust took place under these cratons, the southwestern corner of which on the territory of Belarus is the Vitebsk granulite massif. The article concludes that the Vitebsk granulite massif is the most promising in terms of diamond-bearing on the territory of Belarus, and within its limits – the Smolensk regional deep fault at the intersection of this fault of northeastern striking with the Odessa-Gomel regional deep fault of submeridional striking south of the city of Orsha. Recommendations are given for further study of promising areas in order to determine their diamond content.

Potassium sulfide KFeS2 (hanswilkeite) has been identified in polymineralic inclusions in a diamond from the Udachnaya kimberlite pipe (Siberian craton, Yakutia). This is the second occurrence of hanswilkeite in nature and the first one in mantle-derived samples. Sulfide KFeS2 is monoclinic, the space group—C 2/c. Its crystal structure consists of chains with K in the interstices. The tetrahedra are centered by iron ions and linked by edges, thus forming chains of [FeS2] frameworks. The strongest lines of the electron diffraction powder pattern are 7.05 Å—(200); 5.34 Å (02¯0); and 3.05 Å (22¯0), and the angles between directions are 2¯0/02¯0>—60° and 2¯0/200>—30°. KFeS2 has been found as a discrete phase within polymineralic inclusions consisting of apatite, ilmenite, chondrodite, phlogopite, dolomite, and a fluid phase. The data obtained from the composition of the hanswilkeite (KFeS2) inclusion and other rare minerals (chondrodite, Mg-apatite, Cr-ilmenite) in primary inclusions in a diamond from the Udachnaya kimberlite testify to the important role of metasomatic processes in diamond formation.

Abstract Coupled U‐Pb and trace‐element analyses of accessory phases in crustal xenoliths from the Late Devonian Udachnaya kimberlite (Siberian craton, Russia) are used to constrain Moho temperature and crustal heat production at the time of kimberlite eruption. Rutile and apatite in lower‐crustal garnet granulites record U‐Pb dates that extend from 1.8 Ga to 360 Ma (timing of kimberlite eruption). This contrasts with upper‐crustal tonalites and amphibolites that contain solely Paleoproterozoic apatite. Depth profiling of rutile from the lower‐crustal xenoliths show that U‐Pb dates increase gradually from rim to core over μm‐scale distances, with slower‐diffusing elements (e.g., Al) increasing in concentration across similar length‐scales. The U‐Pb and trace element gradients in rutile are incompatible with partial Pb loss during slow cooling, but are consistent with neocrystallization and re‐heating of the lower crust for

[Display omitted] • Fennoscandia underwent five phases of post-Caledonian regional km-scale exhumation. • Each exhumation episode was followed by formation of a regional peneplain. • Results define a history involving repeated kilometre-scale burial and exhumation. • Tectonic offsets are seen in Norway but in the continental interior effects are more uniform. • Synchronous episodes on adjacent continents imply plate-scale control. The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides only partial documentation of the geological evolution. A more complete understanding is obtained by also considering evidence of rocks that were formerly present but have since been removed. We report apatite fission track data and associated thermal history constraints in 331 samples of Precambrian basement, younger sedimentary cover, Paleozoic and Mesozoic igneous rocks from outcrops and boreholes (up to 6 km depth) across Fennoscandia, which define thirteen phases of cooling (each representing kilometre-scale exhumation) over the last 1100 Myr. Key post-Caledonian episodes began in the intervals 311–307 Ma (late Carboniferous), 245–244 Ma (Middle Triassic), 170–167 Ma (Middle Jurassic), 102–92 Ma (mid-Cretaceous) and 23–21 Ma (early Miocene). These episodes, varying in magnitude, are recognised across Fennoscandia, and their effects are documented in the stratigraphic record and as prominent regional peneplains. The results define a history involving repeated episodes of regional burial and exhumation. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasising the tectonic nature of the history. Results from Finland record the same events recognised in Norway and Sweden (though less pronounced), and are not consistent with long-term cratonic stability. The lack of preserved Phanerozoic sedimentary cover in Finland is interpreted to be due to complete removal during multiple episodes of denudation. In southern Norway and Sweden, early Miocene exhumation led to creation of a peneplain, which in Pliocene times was uplifted and dissected, producing the modern landscape. Post-Caledonian exhumation episodes defined here are broadly synchronous with similar events in Greenland, the British Isles and North America. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here. [ABSTRACT FROM AUTHOR]

Identifying the composition of primary/primitive mantle melts is crucial for understanding the mantle's evolution and mantle‐derived magmatism. Melt inclusions in mantle xenoliths provide key information about such melts. This study used confocal Raman spectroscopy to characterize mineral assemblage of unexposed crystallized secondary melt inclusions in the olivine from the xenoliths of the sheared garnet peridotites from the Bultfontein kimberlite pipe (Kimberley cluster, Kaapvaal Craton, South Africa). The studied peridotites originated from 112‐ to 146‐km mantle depths. In total, 16 minerals were identified among daughter crysatls, which include carbonates (calcite, magnesite, dolomite), alkali carbonates (eitelite, nyerereite, gregoryite/natrite, K–Na–Ca–carbonate (K,Na)2Ca(CO3)2 (K analogue of nyerereite), alkali carbonates with additional anions (northupite, bradleyite, burkeite), alkali sulfates (glauberite, thenardite, aphthitalite), apatite, tetraferriphlogopite, and magnetite. Several more daughter minerals gave distinct Raman spectra, but they were not determined due to the lack of similar spectra in the databases. Carbonates are predominant among the daughter minerals in the melt inclusions. Many daughter minerals are rich in alkalis. These facts indicate that melt(s), parental for the inclusions, is alkali‐rich carbonate in composition. Two possible models were suggested for the origin of these melt inclusions: (1) in situ fracturing of olivine and the mantle melt infiltration shortly before the sheared peridotites were entrained by the ascending kimberlitic magma; (2) infiltration of the transporting kimberlite melt into xenoliths during ascent. Both models imply that the alkali‐rich carbonate melt(s) that interacted with peridotites originated at a greater depth than the entrapment level of studied xenoliths (>150 km), that is, at the base of the lithosphere or in the asthenosphere. This melt is genetically related to the kimberlite magmatism that formed the Bultfontein pipe and points at the alkali‐rich carbonate composition of primary kimberlite melt. [ABSTRACT FROM AUTHOR]

In modern concepts, the upper mantle of the Earth is a highly viscous incompressible liquid, and its flow is described using the Navier – Stokes equations in the Oberbeck – Boussinesq and geodynamic approximations. Convective flows in the upper mantle play a decisive role in the kinematics of lithospheric plates and the geological history of continental regions. Mathematical modeling is a basic method for studying convective processes in the mantle. Our paper presents a numerical model of convection, which is based on the implicit artificial compressibility method. This model is tested in detail by comparing our calculation results with the results of a well-known international test. It is demonstrated that the Fedorenko grids sequence method is highly efficient and reduces the computing time almost by a factor of eight. The numerical model is generalized in order to state the problem in a spherical system of coordinates. It is used to analyse the distribution of convective flows in the upper mantle underneath the Eurasian continent. The analysis shows that the thickness and geometrical parameters of the lithospheric blocks are the factors of significant influence on the distribution of convective flows in the upper mantle. The resulting structure of convective flows is manifested in the surface topography of large platform areas wherein the lithosphere thickness is increased. Thus, the locations of extended downward convection flows under the East European and Siberian platforms are clearly comparable to syneclises observed in the study area.

• Zircon and titanite in xenoliths document Eocene metasomatism of the Wyoming craton lower crust. • Metasomatism by hydrous and carbonated fluids linked to subduction of the Shatsky conjugate and Farallon slab beneath the northern margin of the craton. • Metasomatism, slab foundering, and heating triggered partial loss of the Wyoming craton lithosphere. New zircon and titanite U-Pb and trace-element data from minette- and kimberlite-hosted lower crustal xenoliths from near the northern margin of the Wyoming craton document multiple periods of metasomatism from 62 to 50 Ma. Metasomatism was either coincident or preceded eruption of the host magmas by up to 14 Myr (eruption dated at 52 Ma and 48 Ma based on new zircon U-Th/He data). Thus, fluid/melt interactions were not solely related to magmatic entrainment and eruption. Accessory mineral trace element data reveal metasomatism by fluids from multiple sources, including water and carbonatite potentially sourced from the subducted Farallon slab. These metasomatic episodes are interpreted to reflect pan-lithospheric hydration events that weakened the deep cratonic lithosphere and facilitated partial removal following rollback and foundering of the Farallon plate. The new data corroborate previous suggestions that subduction-related metasomatism may be a key requisite for the destruction of otherwise stable cratons. [ABSTRACT FROM AUTHOR]

Although most economic geology research is concentrated at the deposit or mineral-system scale for a single well-defined deposit group with a consistent metal association, there are both academic and economic advantages in considering the similar geodynamic setting of deposits having contrasting metal compositions that are traditionally considered unrelated. As an example, there are a range of mineral deposit types or systems that are spatially associated with the margins of long-lived, relatively cold, buoyant Precambrian cratons or lithosphere with thick mantle lithosphere roots. These diverse hypogene deposit groups include world-class to giant BIF-derived iron ores, Kiruna-type Fe-P deposits, anorthosite-hosted ilmenite deposits, IOCG deposits, carbonatite-associated REE-P-Nb-(Cu) ores, intrusion-hosted Ni-Cu-PGE sulfide ores, SEDEX (and MVT) Pb-Zn-Cu deposits, Zambian Copperbelt-type Cu-Co, and IOCG deposits, that provide a high proportion of the global metal inventory. Their preservation, some older than 2 Giga-years, is due to the buoyancy of the thick, cold cratonic lithosphere. Deep extensional fault systems develop on these craton margins during rifting, leading to deposition of continental-shelf sedimentary sequences that provide both suitable host rocks for mineralization and metal and sulfur-rich high-salinity fluid sources. The long-lived lithosphere margins with fluctuating stress fields enhance the Pb-Zn-Cu endowment potential of these basins by promoting syn-basinal or later gravity-driven flow of high-salinity brines. Compressional or transpressional reactivation drives syn-orogenic fluid flow to produce the Cu-Co ores of the Zambian Copperbelt, or provide the pre-ore thrust architecture of fluid seals over reactive carbonate sequences for Carlin-type gold ores. The deep faults provided preferred conduits for the emplacement of mafic-ultramafic intrusions, with Ni-Cu-PGE sulfide deposits formed within complexities in the magma plumbing systems. The magmatic–hydrothermal group of carbonatite-related REE-P-Nb-Cu, IOCG deposits, and IRGD systems, and the hydrothermal Carlin-type deposits, all formed under extensional high heat-flow tectonic regimes and derived their ore fluids, with the probable exception of Carlin-type ores, from metal- and volatile-fertilized sub-continental lithosphere below the craton margin. The orogenic gold deposits on craton margins in China were also formed during transpressional geodynamic episodes from ore fluids with a fertilized mantle lithosphere source. A detailed analysis shows that most deposit types are sited within 100 km of the margins of Archean cratons, although sediment-hosted Pb-Zn-Cu deposits, that show no obvious relationships to craton margins, require a buffer of 200 km for thick Paleoproterozoic lithospheric blocks. These features brought out in this paper can potentially aid mineral exploration in terms of initial area selection within the available search space, but precise definition of these buffer zones is difficult due to heterogeneity of constraints on the precise location of craton and thick lithosphere boundaries globally. However, the search space for this diverse group of deposits is limited to between 10 and 35% of the continental crust in different regions, within which geophysical methodologies can further constrain more prospective targets. [Display omitted] • Evaluation of mineral deposits spatially associated with margins of cratons or lithosphere • Deep extensional fault systems play a critical role in the formation of global metal inventory • Novel concepts aiding in mineral exploration and constraining more prospective targets. [ABSTRACT FROM AUTHOR]

The article explores the implications of the thermobarometry of diamond inclusions to the structure of lithospheric mantle and evolution in time and diamond formation. Topics covered include the differences between the Archean diamond inclusions and those found in diamonds from Archeab Proterozoic and other later kimberlites, geochemical evidences for the crytallization of diamonds from protokimberlites, and evidences that diamonds were created at the vicinity of the magmatic systems.

The results of study secondary crystallized melt inclusions in olivine of a sheared peridotite xenolith from the Komsomolskaya–Magnitnaya kimberlite pipe (Upper Muna field, Yakutia) are reported. Monticellite, phlogopite, tetraferriphlogopite KMg3(Fe3+)Si3O10(F,Cl,OH), apatite, aphthitalite K3Na(SO4)2, burkeite Na6CO3(SO4)2, and carbonates, namely calcite, nyerereite (Na,K)2Ca(CO3)2, shortite Na2Ca2(CO3)3, and eitelite Na2Mg(CO3)2, were detected among the daughter minerals of the melt inclusions by the method of confocal Raman spectroscopy. The abundance of alkali carbonates in the inclusions indicates the alkali–carbonate composition of the melt. Previously, identical inclusions of alkali–carbonate melt were reported in olivine of sheared peridotites from the Udachnaya pipe (Daldyn field). Melt inclusions in sheared peridotites are the relics of a crystallized kimberlite melt that penetrated into peridotites either during the transport of xenoliths to the surface or directly in the mantle shortly prior to the entrapment of xenoliths by the kimberlite magma. If the second scenario took place, the finds of alkali–carbonate melt inclusions in sheared peridotites carried from different mantle depths in the Udachnaya and Komsomolskaya–Magnitnaya kimberlite pipes indicate a large-scale metasomatic alteration of the lithospheric mantle of the Siberian Craton by alkaline-carbonate melts, which preceded the kimberlite magmatism. However, regardless of which of the two models proposed above is correct, the results reported here support the alkali–carbonate composition of primary kimberlite melts. [ABSTRACT FROM AUTHOR]

The interpretation of low‐resistivity anomalies in the lithospheric mantle of several cratonic regions has invoked hydrogen, or connected networks of graphite with iron‐rich silicates, and/or metal sulfides. Electrical laboratory measurements are a powerful approach for exploring these alternatives. We report electrical measurements of two xenoliths (pyroxenite and dunite) from Tanzania; two metal sulfides (FeS and Fe‐S‐Ni); and several mixtures of metal sulfides (3.4–18.2 vol.%) with xenolith. A multi‐anvil press was employed to maintain a 2 GPa pressure and temperatures up to 1,627 K. The addition of 3.4 vol.% FeS to the pyroxenite or dunite matrix has little effect on bulk resistivity, particularly for T > 800 K. However, the resistivity drops dramatically–by factors of up to 1,000, depending on temperature–upon addition of 6.5 vol.% FeS in the dunite. Addition of 18.2% FeS causes a further decrease of the same magnitude relative to the 6.5% sample. Scanning electron microscope images do not reveal the formation of a connected FeS network as part of the decreased resistivity. Possible explanations for the apparently conflicting results include connections of the sulfide that are not imaged in the back‐scattered images, either because of limited resolution, or perhaps the inherent limitations of the 2‐D perspective. The complete data set (xenoliths, metal sulfides, and mixtures) was modeled with a modified version of Archie's law, and we find satisfactory agreement over a truncated temperature range. We conclude that the low‐resistivity anomalies in Tanzania, Kaapvaal, and Gawler cratons can be explained by the presence of a few vol.% of solid sulfide. Plain Language Summary: Some regions in the cold and stable parts of the Earth's upper mantle have exceptional electrical properties; they are very conductive. What causes these anomalies is not well understood, and one explanation could be the presence of iron‐sulfur compounds. Here we tested this hypothesis by performing electrical experiments under pressure and temperature on natural and synthetic mantle rocks. The amount of iron‐sulfur compound was varied to understand its effect on the electrical properties. Our results show that a small amount of iron‐sulfur compound can affect the electrical properties of the upper mantle dramatically. We then modeled our data to apply these results to the field. We conclude that the electrical anomalies in Africa and Australia can be explained with a few volume % of solid iron‐sulfur compound in the mantle rock. Key Points: The resistivity of sulfide‐xenolith samples at 2 GPa drops by a factor of up to 1,000 for an addition of FeS between 3.4 and 6.5 vol.%A fully connected network of the FeS phase is not necessary to achieve significantly lowered bulk resistivityLow‐resistivity anomalies in several cratons can be explained with a few vol.% of solid sulfide [ABSTRACT FROM AUTHOR]

The Ordos Block is located at the intersection of the Tibetan Plateau, the South China Plate and the North China Craton. The deep deformation of its surrounding areas is geologically complicated. Seismic anisotropy provides information about past and present deformation of the upper mantle and helps to better understand deep deformation processes. We obtained the anisotropic pattern at high resolution within and surrounding the Ordos Block by analysing teleseismic data from ∼710 newly deployed temporary seismic stations based on SKS phases from ∼86 earthquakes. The central and eastern Ordos Block with a relatively thick and rigid lithosphere is characterized by a weak anisotropy. In the western part of the Ordos Block, the fast-wave polarization direction is dominantly NW–SE. We believe the lithosphere in the western part of the Ordos Block may have undergone significant deformation caused by expansion and compression of the Tibetan Plateau. Near the Datong Basin, the delay time is 0.92 s and the fast-wave polarization direction is mainly oriented NW–SE, perpendicular to the NE-directed compression of the Tibetan Plateau and parallel to the basin extension direction. We speculate that this anisotropy is related to the long-range effect of NE compression of the northeastern Tibetan Plateau on the low-velocity upper mantle in this area. The weak anisotropy in the central part of the Shanxi Rift indicates that the thickness and mechanical strength of the high-velocity lithosphere are higher than in the southern and northern regions. [ABSTRACT FROM AUTHOR]

The factors that promote stability of Archean cratons are investigated from a combined geodynamic, geological, and geophysical perspective in order to evaluate the relative importance of nature—the initial conditions of a craton—versus nurture—the subsequent tectonic processes that may modify and destabilize cratonic lithosphere. In this review study, we use stability regime diagrams to understand the factors that contribute to the intrinsic strength of a craton: buoyancy, viscosity, and relative integrated yield strength. Cratons formed early in Earth history when thermal conditions enhanced extraction of large melt fractions and early cratonization (cessation of penetrative deformation, magmatism, and metamorphism) promote formation of stable Archean cratonic lithosphere. Subsequent processes that may modify and weaken cratonic lithosphere include subduction and slab rollback, rifting, and mantle plumes—processes that introduce heat, fluids, and partial melts that warm and metasomatize the lithosphere. We examine tomographic models from eight cratons, including four that are thought to be stable and four that have been proposed to be modified or destroyed. Our review suggests that continental lithosphere formed and cratonized prior to the end of the Archean has the potential to withstand subsequent deformation, heat, and metasomatism. Survivability is enhanced when cratons avoid subsequent tectonic processes, particularly subduction. It also depends on the extent and geometry of modification. However, because craton stability decreases as the Earth cools, marginally stable cratons that undergo even modest modification may be set on a path to destruction. Therefore, preservation of Archean cratons depends both on nature and nurture. Plain Language Summary: Because of Earth's dynamic tectonic processes, much of its continental crust has been eroded and recycled and only a fraction of crust older than 2.5 billion years has survived to the present‐day. These areas of old crust, known as Archean cratons, have not experienced deformation or magmatism for a billion years or more. This study investigates whether craton survival is related to their nature, that is, the conditions of their formation, or to nurture, the subsequent events they experienced. Eight case studies are used to evaluate the properties and processes that promote craton stability. Nature is important: surviving Archean cratons tend to be buoyant, viscous, cold, and thick. Some survive because they have not experienced destabilizing geologic processes that introduce heat, magma, and fluids. Others have been modified to various extents by these processes. Some have been weakened and thinned and other, only marginally stable cratons are susceptible to future deformation and destruction. We conclude that both nature and nurture are essential to the survival of Earth's oldest crust. Key Points: The survival of Archean cratons depends both upon their nature—the initial conditions of formation—and nurture—the subsequent tectonic processes that may modify and destabilize cratonic lithosphereSome cratons have survived by avoiding or being shielded from destabilizing tectonic processes. Metasomatism is particularly destructive because it affects buoyancy, viscosity, and integrated yield strengthStability regime diagrams integrate both time and the magnitude of modification, and indicate that marginally stable cratons today may pass into conditions of marginal instability in the future, when even mild deformational stresses could trigger destruction [ABSTRACT FROM AUTHOR]

We use splitting in core‐refracted teleseismic shear waves (SKS, PKS, and similar) to investigate anisotropic properties of the upper mantle beneath the Superior craton in eastern North America and the Yilgarn craton in Western Australia. At four sites in each craton, we assemble extensive data sets that emphasize directional coverage, and use three different measurement methods to develop mutually consistent constraints on the nature of splitting and on the likely anisotropic properties that cause it. In both cratons, we see evidence of clear directional variation in both delays and fast polarization directions, as well as lateral differences between sites. Relatively small (0.3–0.8 s) amounts of splitting imply weak anisotropy within 150–220 km thick mantle lithosphere. Anisotropy in the asthenosphere likely contributes to splitting in North America where fast directions align with absolute plate motion, but not in Western Australia where fast polarizations and plate motion are nearly orthogonal. Plain Language Summary: Cratons, areas of the continents that did not deform for a billion years or more, are the only record of the geological events from the first half of Earth's existence. Large‐scale deformation of the rigid lithosphere of cratons is expected to imprint a systematic fabric within its rocks. This fabric makes the speed of seismic waves dependent on direction (anisotropic) and causes birefringence (splitting) in horizontally polarized (shear) waves from distant earthquakes. Surprisingly low level of birefringence is seen in many cratons, suggesting weak anisotropy and by inference—a poorly developed systematic fabric within them. Alternatively, competing effects of fossil anisotropy in the lithosphere and the anisotropy due to present‐day deformation beneath it can result in cancellation of birefringence. We measured splitting in large data sets from the Yilgarn craton of Western Australia and the Superior craton in eastern North America. We confirm the small amount of splitting in both areas and rule out mutually canceling effects of anisotropy within and beneath the lithosphere. This suggests weak anisotropy in the lithosphere of both cratons. Directions of tectonic plate motion suggest that anisotropy due to deformation beneath the lithosphere affects our measurements in North America but not in Australia. Key Points: Three consistent methods are used to measure splitting in core‐refracted shear waves in Yilgarn and Superior cratonsSmall amount of splitting in both regions is found indicating weak anisotropy in both cratons' lithosphereAnisotropy in the asthenosphere likely contributes to splitting in the Superior but not in the Yilgarn [ABSTRACT FROM AUTHOR]

The Sm–Nd isotope systematics and geochemistry of eclogitic, websteritic and peridotitic garnet and clinopyroxene inclusions together with characteristics of their corresponding diamond hosts are presented for the Letlhakane mine, Botswana. These data are supplemented with new inclusion data from the nearby (20–30 km) Orapa and Damtshaa mines to evaluate the nature and scale of diamond-forming processes beneath the NW part of the Kalahari Craton and to provide insight into the evolution of the deep carbon cycle. The Sm–Nd isotope compositions of the diamond inclusions indicate five well-defined, discrete eclogitic and websteritic diamond-forming events in the Orapa kimberlite cluster at 220 ± 80 Ma, 746 ± 100 Ma, 1110 ± 64 Ma, 1698 ± 280 Ma and 2341 ± 21 Ma. In addition, two poorly constrained events suggest ancient eclogitic (> 2700 Ma) and recent eclogitic and websteritic diamond formation (< 140 Ma). Together with sub-calcic garnets from two harzburgitic diamonds that have Archaean Nd mantle model ages (TCHUR) between 2.86 and 3.38 Ga, the diamonds studied here span almost the entire temporal evolution of the SCLM of the Kalahari Craton. The new data demonstrate, for the first time, that diamond formation occurs simultaneously and episodically in different parageneses, reflecting metasomatism of the compositionally heterogeneous SCLM beneath the area (~ 200 km2). Diamond formation can be directly related to major tectono-magmatic events that impacted the Kalahari Craton such as crustal accretion, continental breakup and large igneous provinces. Compositions of dated inclusions, in combination with marked variations in the carbon and nitrogen isotope compositions of the host diamonds, record mixing arrays between a minimum of three components (A: peridotitic mantle; B: eclogites dominated by mafic material; C: eclogites that include recycled sedimentary material). Diamond formation appears dominated by local fluid–rock interactions involving different protoliths in the SCLM. Redistribution of carbon during fluid–rock interactions generally masks any potential temporal changes of the deep carbon cycle. [ABSTRACT FROM AUTHOR]

Abstract The goal of this study is to constrain the origins of layering in the seismic velocity structure within the cratonic mantle lithosphere (i.e. mid‐lithospheric discontinuities [MLDs]). For long‐lived stations in cratons worldwide, we calculated S‐to‐P converted phase receiver function stacks using time domain deconvolution and a k‐means algorithm to select robust, consistent receiver functions. Negative MLDs appear in only 50% of the receiver function stacks, indicating that negative MLDs are common but intermittent. The negative MLDs correspond to shear velocity drops of 1%–4%, which could be caused by layers of minerals created by metasomatism, although vertical layering in seismic anisotropy cannot be ruled out. In craton interiors, negative MLDs have a lower amplitude (

Abstract Seismic anisotropy provides insight into past episodes of lithospheric deformation and the orientations of strain in the underlying asthenosphere. The Greenland mantle has played host to a rich history of tectonic processes, including multiple orogenies and plume‐lithosphere interactions. This study presents new measurements of SKS splitting that reveal strong variations in fast polarization direction with back‐azimuth that are consistent across Greenland, including at stations where splitting measurements have not previously been reported. We compared observed fast polarization directions to the predictions of two‐layer models with olivine‐orthopyroxene anisotropy. The family of models that provides acceptable misfits at 95% confidence indicates an upper layer olivine a‐axis azimuth of 222–236°, a lower layer olivine a‐axis azimuth of 114–130°, and non‐zero a‐axis plunges. These models are consistent with an upper layer of lithospheric anisotropy due to Proterozoic and Archean orogenic fabrics, and a lower layer of anisotropy corresponding to either asthenospheric flow aligned approximately parallel to the direction of absolute plate motion and plunging due to lithospheric topography or dipping lithospheric structures created by episodes of paleo‐convergence.